An uninterruptible power supply (UPS) is a type of power supply used to power and protect an electrical load that is sensitive to fluctuations in or the absence of electrical power. The UPS can be connected between the load and a source of electrical power, such as a mains power source or other commercially provided electric power. The UPS uses commercially supplied AC power to charge a DC battery and provide the AC power to load. Upon outages of power, the load draws its AC power from the DC battery through the DC to AC inverter. This isolates the load from power surges or brownouts and also furnishes a source of power during brief outages.
Commonly, a UPS comprises a rectifier, inverter, battery charger, DC battery, and other components, all housed within a single case or package. FIG. 1 shows a typical prior art UPS 1 used to provide regulated uninterrupted power. The UPS 1 includes an input filter/surge protector 2, a transfer switch 3, a controller 4, a battery 5, a battery charger 6, an inverter 7, and a DC—DC converter 8. The UPS also includes an input 9 for coupling to an AC power source and an outlet 10 for coupling to a load.
The UPS 1 operates as follows. The filter/surge protector 2 receives input AC power from the AC power source through the input 9, filters the input AC power and provides filtered AC power to the transfer switch 3 and the battery charger 6. The transfer switch 3 receives the AC power from the filter/surge protector 2 and also receives AC power from the inverter 7. The controller 4 determines whether the AC power available from the filter/surge protector is within predetermined tolerances, and if so, controls the transfer switch to provide the AC power from the filter/surge protector to the outlet 10. If the AC power from the rectifier is not within the predetermined tolerances, which may occur because of “brown out,” “high line,” or “black out” conditions, or due to power surges, then the controller 4 controls the transfer switch 3 to provide the AC power from the inverter 7. The DC—DC converter 8 is an optional component that converts the output of the battery 5 to a voltage that is compatible with the inverter 7. Depending on the particular inverter 7 and battery 5 used the inverter 7 may be operatively coupled to the battery 5 either directly or through a DC—DC converter 8.
As consumer electronic products such as computers, become more widespread, smaller, lightweight, and less expensive, there has been a corresponding increase in the need for smaller, lighter, lower-cost UPS systems. However, designers of electronic instruments such as UPS's typically have focused their energies on reducing the size and cost of the components contained within the device rather than redesigning the chassis or housing of the instrument. Thus, presently available UPS devices still take much time to assemble and require many connectors and fasteners that increase both weight and manufacturing cost. In addition, because parts such as batteries and transformers are heavy and awkward to install, it is difficult to design a simplified, lightweight UPS enclosure capable of securely containing such components.
Known enclosures and chassis designs for a UPS commonly include a metal frame having several partitions or walls to which the components are mounted or attached. The frame itself can be fastened to an outer device housing. Manufacturing the prior art chassis for a UPS is a relatively complicated and time-consuming process. For example, making a metal chassis often requires stamping and bending metal sheets. The surfaces of the sheets may be treated, for example by galvanizing, before connecting the sheets to each other by an appropriate connection method, such as screwing, welding, riveting, adhesives, or a combination of these methods. Components are connected to the chassis by fastening elements like screws or rivets or other connection techniques. Sometimes components are connected to the sheets before the sheets are assembled together.
It is also known to use hard plastic parts to form a chassis, but known plastic chassis designs nonetheless result in a complicated and time-consuming assembly process, because the fastening elements still must be attached to the chassis, for example by ultrasound welding, gluing, or pressing. Moreover, it is less common to use known plastic chassis designs for electronic devices such as UPS's, which typically include very heavy components such as transformers and batteries. These heavy components (and even the relatively lighter components, such as printed circuit boards (PCBs), often require additional holding members, such as brackets or angle plates, to hold the component securely at the preferred position within the chassis. The holding members add to the weight, cost, and complexity of the chassis.
Thus, making a chassis for electronic instruments such as a UPS and assembling its components to it is costly and time-consuming, requiring the use of mounting tools, such as screw drivers, bending tools, riveting tools, welding tools, or adhesive dispensers. Metallic enclosures add an unnecessary amount of weight to the electronic instrument, but known plastic enclosures still require supporting members, if they are to be used with electronic instruments having particularly heavy components.